Questions tagged [radio-frequency]

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1answer
33 views

How to read a meter for radio and microwaves?

I am not clear on how to read this meter for radio waves and microwaves. The bottom band shows it measures from .01 to 1. First, I'm not sure what the units mean (mW/cm2). Radio waves are from 30KHz-...
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1answer
123 views

What piece of technology is able to record the exact phase of microwaves?

I read that in VLBI, the signals of microwaves are recorded and then later combined. A famous example of this is the Event Horizon Telescope which imaged the black hole. Presumably, the telescopes ...
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2answers
63 views

How far can an x-ray travel through water?

I am studying x-ray's and how they interact with different mediums, but I am a bit confused on the distances an x-ray can travel through different mediums such as water. Let's take an x-ray with 3 ...
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23 views

Commercial Radio Bandwidths around the world

I'm a liberal arts person who has more than a passing interest in radio but it has taken years for this to dawn on me, so be kind if it is obvious. I was out of the US recently, and I saw a radio in ...
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1answer
51 views

How much can gravity affect light frequency?

I was wondering, maybe SETI cannot catch alien radio signals, because they don't monitor the right wavelengths. What if aliens live near a black hole or a denser region and radio signals coming from ...
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3answers
86 views

How gravity time dilation affect radio wave communication?

I'm not in any way an expert so sorry if my question is silly. So i was wondering about a hypothetical situation. I'm orbiting a black hole and I'm trying to contact via radio with someone outside the ...
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19 views

What is the relationship between average pulsar amplitude and the frequency?

Hi my question is pretty much in the title when im referring to frequency im referring to the frequency of the pulses. I have plotted a graph frequency vs average pulse amplitude but i don't ...
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1answer
31 views

Klystron output voltage, cavity physics

Can you please explain why almost nowhere do I see such a parameter as the output voltage from a klystron, it's easy to find the DC accelerating voltage of the beam and the electron bunch densities ...
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1answer
24 views

Wave Interference (Control Tower vs Mobile Phones)

I was curious about something regarding radio waves. When we're talking about differences of 200 MHz between waves, is there any way of any noticeable interference occurring? By noticeable I mean ...
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1answer
67 views

Can a lower frequency receiver antenna receive information from a higher frequency signal?

End goal: I wish to use a smartphone NFC transmitter (high-frequency RFID @ 13.56 MHz) to send data to a low-frequency RFID @ 120–150 kHz door reader to open the door. Illustrative example: HF ...
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2answers
45 views

Are radio waves naturally produced?

I am just wondering if radio waves are naturally produced. If so how?
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1answer
33 views

Irradiation at high frequency

I read this statement in Feynman Lecture on Physics (see here for more details): In low-frequency circuits the connection is made with wires, but this method doesn’t work very well at high ...
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0answers
39 views

Total thermal noise of a photodetector connected to a spectrum analyzer

I connected a photodetector to a spectrum analyzer (SA) and observed the signal (i.e. noise) on the SA when there is no light hitting the detector. I noticed that when I set a low spectral resolution ...
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0answers
60 views

How can cell phone towers transmit despite the rain?

I once read that waves of higher frequency (such as around 1 GHz range and higher) have difficulty passing through water (or other liquids/solids). Today, when I saw a cellphone tower, I wondered: "...
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0answers
25 views

Changing the refractive index of biological tissue using Radio Frequency (RF)

I have been looking into changing the refractive index of a specific medium initially using Ultrasound in a known location via a mechanical Doppler shift of the emitter (Mahan et al., 1998) which has ...
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37 views

Permeability of the human skull using Radio Frequency (RF) and Ultrasound waves

I have been looking into the permeability of the human skull using RF and ultrasound waves, and had a few questions. Which frequencies of Ultrasound and Radio Frequency (RF) waves can pass through ...
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30 views

Changing the refractive index of a specific medium using radio frequency (RF) waves

Using Ultrasound one can change the refractive index of a specific medium such as biological tissue, I was wondering if it is possible to change the refractive index of a medium such as biological ...
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0answers
36 views

Red shift of radio signals

If a radio signal is red-shifted does it still last the same amount of time? Knowing the signal wavelength is now longer but still is traveling at the speed of light one would assume the radio message ...
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1answer
121 views

How did German radio beams reach distant English cities during WWII? [closed]

During WWII, the Germans were using radio beacons (the "Knickebein" system) to guide their bombers into English territory. They set up two beacons, one in Kleve, a city in West Germany, and one at ...
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21 views

RF Transmission Loss

I am aware that an ideal 3rd order circuit with R=0 will oscillate forever, but even this this is not true. Power is dissipated through the em waves. How does one calculate the losses due to these ...
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1answer
27 views

Is the radio attenuation of an obstructed 2.4GHz signal, dependent on its incident power?

The following figure (taken from CTS 115: Free Space Path Loss) describes generally how obstructions attenuate a 2.4GHz signal: I would like to ask, is this -3dB loss dependent on the power (or ...
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2answers
46 views

Radio wavelength to penetrate 8 ft of seawater

I am trying to penetrate about 8 ft of seawater with a radio wave. What wavelengths will work? I understand that low wavelengths penetrate seawater the best, but I am looking for a frequency that does ...
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1answer
55 views

How to calculate how far radio light goes in the ocean [closed]

Radio light is not a practically useful way of communicating underwater over large distances. My question is how does one calculate how far a radio wave at a given frequency will propaagate in the ...
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1answer
36 views

Does the effect at Brewster's angle apply for all angles greater, or only at that angle?

Came across Brewster's angle while studying radio frequency propagation. something I'm unclear about is whether or not the polarizing effect only happens at Brewster's angle, or if it continues for ...
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23 views

Why cant a wire emit light if we apply high enough electric frequency to it? [duplicate]

From my understanding of physics radio and light is the same but with different frequency. Why then there is no lightsource yet made of just a wire and high frequency generator?
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6answers
171 views

Why are we looking for alien signals from radio waves?

Is the only reason we are scanning the radio frequency bands for signs of aliens simply as this is all we have technologically able to do? It seems that any civilization capable of interstellar ...
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2answers
57 views

Radio Waves / Light: Atmospheric Refraction

The following image differentiates between a visual horizon and a radar horizon. Sidenote: I'm not too familiar with primary surveillance radar technology, but this image refers to secondary ...
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1answer
85 views

Why aren't extremely-low-frequency (ELF) radio waves used for underwater radar?

Since extremely-low-frequency radio waves are used by submarines for some simple, low-transmission-rate communications, why can't those same wavelengths be used for submarine radar? It may not be ...
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1answer
44 views

Strange strong interference/noise in radio waves [closed]

Good night, Since 2014 when I bought my car I use a FM transmitter inside it to play my bluetooth musics, to escape for every radio in city I put the radio to work in the highest frequency it works ...
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0answers
48 views

Would a radio frequency (RF) laser have any advantage over ordinary radios?

In the radio part of the electromagnetic spectrum it is really easy to make very clean and powerful RF waves using modern electronics, and it really isn't that hard to make arbitrary RF waves. But ...
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1answer
83 views

How does Event Horizon Telescope filter to get only the radio waves emitted by the target black hole?

There are many stars and black holes in the universe. So, their emitting radio waves may be mixed in the universe. How did the event horizon telescope filters to get only the radio waves emitted by ...
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0answers
23 views

The effect of dielectric bridges on the impedance of a coplanar waveguide

I'll start with some context, but feel free to skip to the third paragraph for the concrete question. I also posted it on the electronics stackexchange, but I think it might have some more chance here ...
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0answers
30 views

Power from human vs solar radio waves

I'm looking for a nicely presented comparison of solar radio waves and human-generated radio waves. The parameter I am most interested in is power. I imagine that human-generated radio waves exceed ...
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3answers
1k views

Could you use a laser beam as a modulated carrier wave for radio signal?

There have been successful experiments in modulating sound over a carrier ultrasound wave. Not so long ago, I've even seen an DIY implementation on Hackaday. I also encountered and tested a program ...
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3answers
305 views

Can radio waves be harmful to us?

I was studying about Microwaves and their action on water molecules in heating up the food. This all is probably due to Microwaves have wavelength such that it can be absorbed by water molecules (am i ...
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1answer
35 views

About sound of non-existent channels on FM

Well, I have learnt about resonant frequency due to series capacitor and inductor, and how the current at resonant frequency is highest, but i am confused about the sound, which appears even when no ...
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1answer
33 views

Identify the frequency antenna I can't access

I recently bought a (used) radio controlled airframe and buried deep inside the tail section is an antenna, broken out to some coax, with an SMA connector within the core of the fuselage. There is no ...
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1answer
66 views

How do LF Radio waves send data?

Excuse me I am a complete beginner. If LF radio waves are sent with let’s say frequencies of 100 kHz, how can data be modulated to that signal considering the signal is so long? For example, how can ...
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1answer
77 views

Why does S11 seem to be independent of transmission media in this RF transmission experiment?

Hi friends I am starting to characterize a system in which we will plan to measure the response of a sample of liquid to radio waves. In order to do this I am exciting two antennas with the ports of ...
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1answer
47 views

How RF receivers receive waves with bigger wavelenght than the distance between them?

I have a 27MHz RF toy car and I was wondering since the wavelenght is about 11 meters, when the car is closer to the remote than 11 meters how does the car receive the signal? Wouldn't the signal be ...
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3answers
86 views

Why do sensors that emit higher frequency signals give more accurate data?

I am doing a technical presentation about RADAR and LiDAR. I understand that LiDAR is several times more accurate and capable of producing really detailed 3-D maps of their surroundings, while RADARs ...
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1answer
50 views

Best cantenna reflector type

If the reflector (closed end) of cantenna is shaped as parabolic dish, will it perform better than one with a flat reflector?
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1answer
66 views

Why is $Q$ factor an important quantity for electrical oscillations transmitting radio waves?

My textbook says that "$Q$ factor is an especially important quantity for electrical ossicilations trasnmitting radio waves. When selecting radio and television stations it is essential that the ...
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1answer
36 views

How can I calculate the total rotation a detuned pulse will apply a nuclear spin?

I'm trying to model the effect a radiofrequency pulse will have on a nuclear spin at different detunings. The pulse has a sech lineshape, a pulse area (time integral of the pulse envelope) of $\frac{π}...
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3answers
463 views

Can a lens be used at radio frequency?

Lenses and Antennas are two means of manipulating EM waves. While antennas are predominantly used at RF / Microwave frequencies, Lenses are used for optical/IR regions of the spectrum. I understand ...
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38 views

Are there Lasers in wavelenght of UHF or radio frequency?

how exists lasers in many wavelength in electromagnetic spectrum, like UV, VIS and IR. I don't know nothing about others wavelength as X-ray or radio frequency.
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2answers
80 views

How can Line of Sight work?

How can a mobile phone work inside a closed room with no openings if Line of Sight requires no obstacles between the receiver and transmitters? I know you may think it's not a Physics question but ...
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2answers
816 views

Why radio waves from radio-stations don't interfere with each other?

I know that radiowaves from radiostations are modulated either F.M or A.M . Lets suppose they are F.M and one has carrier wave frequency of 100 Hz and other 200 Hz they have F deviation of 20Hz/V . ...
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1answer
153 views

Does attenuation to RF waves increases with frequency?

I heard somewhere that RF waves at high frequency such as above 2GHz face more attenuation while passing through air, buildings and due to humidity as compared to 800Mhz and 2) Waves at 30-40GHz ...
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2answers
112 views

How are RF Waves transmitted?

What is the mode of transmission for RF waves at 1800 MHz. Is it ground wave propagation, Line of Sight Propagation or Atmospheric reflection (from ionosphere). What are the different ways for ...